April 19, 2007 — Spatial neglect, a common poststroke disability, has been linked to impaired communication between attention networks in the dorsal and ventral frontoparietal areas of the brain, a finding that generates a new understanding of how damage in 1 region of the brain affects others.

In a study published in the March 15 issue of Neuron, investigators at Washington University School of Medicine, in St. Louis, Missouri, found a consistent link between the severity of spatial-neglect symptoms and the degree of impairment in communication within and between these 2 largely separate communication networks.

"Spatial neglect is a devastating syndrome, and for many years we thought it was solely due to lesions in specific regions of the brain that were visible on imaging scans. However, one of the things we discovered is that the brain is highly interconnected, and as a result, a lesion in 1 part of the brain not only damages the function of the region where it occurs but also affects other distant areas [of the brain] it is connected to," principal investigator Maurizio Corbetta, MD, told Medscape.

Critical Mechanism

According to the investigators, strokes that cause spatial neglect frequently result in structural damage to the ventral network while sparing the dorsal network. However, a study published by Dr. Corbetta and colleagues in 2005 showed patients with spatial neglect have a functional imbalance of evoked responses in the left and right dorsal parietal cortex, even though these areas are structurally intact.

"We found that these so-called 'distant effects' did have an impact on patients' function and that people with more imbalance in their activation have more neglect. We also found that as they recovered, this degree of imbalance between the left side and the right side of the brain also improved and so did patients' behavioral function," he said.

In the current study, said Dr. Corbetta, the investigators specifically looked at the communication between the ventral attention network and the dorsal attention network and were able to describe the correlation of activity between them.

To do this, they had group of 11 patients who had suffered a right hemispheric stroke resulting in spatial neglect complete a visuospatial attention task while undergoing functional connectivity magnetic resonance imaging (FC MRI) at 1 month and again more than 6 months following stroke.

The results "showed that disrupted functional connectivity in the dorsal and ventral attention networks constitutes a critical mechanism underlying the pathophysiology of neglect."

Promising Investigational Tool

The findings also reinforce the investigators' network hypothesis that injury in 1 part of the brain can damage processes between brain regions essential for the regions' proper function.

Further studies to determine whether other stroke-induced deficits, such as aphasia, are linked to similar disruptions of communication between brain regions are planned.

In addition, said Dr. Corbetta, FC MRI is a promising investigational tool that may eventually make it possible to provide a more accurate prognosis in stroke patients or individuals with other types of brain injury or disease based on functional information.

He added that FC MRI also offers other advantages — it takes very little time and it can be done when patients are at rest.

"The beauty of this [technique] is we can see this network even when patients are quietly lying in the scanner with their eyes closed. It doesn't require patients to interact. This is really very important, because this new way of scanning allows us to study acute or very severe patients, something we weren't able to do before," he said.

Neuron. 2007;53:905-918.